Hitherto, as a process for producing D-2-amino-2-(1,4-cyclohexadienyl)acetic acid, a process for reducing D-2-aminophenyl-acetic acid with metallic lithium and t-butyl alcohol in liquid ammonia (U.S. Pat. No. 3,682,981) and a process for reducing D-2-aminophenylacetic acid with metallic sodium and an alcohol in liquid ammonia (Spanish Pat. No. 419,123) have been known.
However, since in the process disclosed in U.S. Pat. No. 3,682,981, it is necessary to use an expensive metallic lithium, the process is economically unprofitable, and on the other hand, there is a demerit in the process disclosed in Spanish Patent 419,123 that the rate of reduction of D-2-aminophenylacetic acid is low.
Moreover, since in these publicly known processes an alcohol is used as a proton donor for the reaction of reduction, the alcohol must be recovered industrially after the reaction is over, and the following procedures are adopted for the recovery of alcohol:
After decomposing alcoholate of metallic lithium or metallic sodium, which has formed in the reaction system, by triethylamine hydrochloride, ammonia in the reaction system is evaporated off, and the unreacted D-2-aminophenylacetic acid and the reaction product, D-2-amino-2-(1,4-cyclohexadienyl)acetic acid, which remain in the system as a mixture with the alcohol in a state of slurry are heated to evaporate the alcohol to be recovered.
However, such a method of recovering the alcohol by evaporation might lead D-2-aminophenylacetic acid and D-2-amino-2-(1,4-cyclohexadienyl)acetic acid remaining in the above-mentioned mixture into racemization. For preventing such racemization, it is necessary to evaporate the alcohol in the mixture under a reduced pressure at a relatively low temperature to be recovered, and in such a case of evaporation of alcohol under a reduced pressure, D-2-aminophenylacetic acid and D-2-amino-2-(1,4-cyclohexadienyl)acetic acid in the mixture are entrained as a solid matter with the evaporating alcohol, and accordingly, the effective recovery of the alcohol is difficult.
In consideration of the demerits of the publicly known processes which use an alcohol in the production of D-2-amino-2-(1,4-cyclohexadienyl)acetic acid, the present inventors have studied processes for effectively producing D-2-amino-2-(1,4-cyclohexadienyl)acetic acid from D-2-aminophenylacetic acid, and have attained the present invention.